Previous research has demonstrated that visual attention can be spatial or object-based, and that visual working memory (WM) has both spatial and object components. Oh and Kim (2004) demonstrated that loading spatial WM interfered with visual search efficiency but loading object WM did not, suggesting that spatial attention and spatial WM engage similar resources. The present study investigated the effects on object-based attention of loading object WM versus spatial WM. Three tasks were performed in separate blocks (memory baseline, object baseline, dual-task); during all tasks, participants rehearsed aloud a set of digits to prevent verbal rehearsal. In the memory baseline, four to-be-remembered colored squares could appear in eight possible locations and eight possible colors. Subjects a made speeded response to a test probe indicating its match/mismatch to the color (Experiment 1) or location (Experiment 2) of one of the items in WM. In the object baseline (Duncan, 1984), two overlapping objects (a line and box) appeared that could each vary on two dimensions: line tilt (left/right) and texture (dashed/dotted), box size (large/small) and gap location (left/right). Subjects monitored two dimensions either from the same or different objects and made a speeded response indicating the attribute of one of the monitored dimensions. In the dual-task condition, subjects performed both tasks concurrently. As expected from past literature, there was an accuracy cost (reflecting object-based attention) when subjects monitored dimensions from different objects compared to the same object. Compared to the object baseline, there was greater cost in the dual-task condition when color but not location was maintained in WM, even though maintaining location was more difficult as reflected in higher Experiment 2 RTs. These findings suggest that spatial WM and object WM influence object-based attention differently, and that object WM and object-based attention engage similar resources.